A central tracking system represents one of the key elements
of the CMS. The primary goal is to reconstruct all high Pt muons
and isolated electrons in central rapidity region with a momentum
precision of (Tev). The high momentum precision is a
direct consequence of high magnetic field (4T). Taking into account
the multiplicity (about 500 background low energy tracks accompanying
interesting events) the problem of pattern recognition becomes
essentially hard. High granularity of the system is necessary
with a cell size of about 50 µm near the beam line (20-40 cm) and
200 µm at a distance of (40-120 cm). From occupancy considerations
(probability of coincidences in one cell should be less than 1%),
the length of strips should be less than 10 cm in a close region
and less than 20-25 cm in a far region. For a good track reconstruction
the system has to provide about 12 track points in the barrel
and 15-20 in the forward region. The radiation environment in the
central region is very hard. Equivalent flux of charged particles
at 40 cm from the beam is close to 105 mm-2 s-1 which gives 1
MRad/year of integral dose. These two values demand the tracker
to be rate capable and radiation hard.

Novosibirsk group is participating in the "hottest"
part of the Gas Microstrip Tracker
(see Fig.8.1)
in the forward
region (r = 40-80 cm, z = 120-300 cm). This region represents the
highest flux and radiation dose in the MSGC tracker as all low
energy background will concentrate along the beam line due to
high magnetic field. Forward parts of MSGC tracker will consist
of wheels of glass microstrip plates with strips in radial direction.
Microstrip structure in each plate has thin ~7 µm anode strips and
thicker ~70 µm cathode strips. Average strip pitch is 200 µm. In
the inner region of the wheel (r<=60 cm) the plates will be 5 x 10
cm in size while at larger radius from the beam the size of the
plates will be ~10 x 10 cm.

8.3 Research and development

To solve the problem of high rate capability and radiation hardness
we are developing the technology which uses electronically conductive
glass as a substrate and gold as a material for the strips. It
was proven earlier in multiple studies that the substrate which
has some conductivity behaves more stable than the ordinary glass
and that gold as a material for the strips is the best from radiation
hardness point. Budker INP together with NIIES (Moscow) developed
glass with the required resistivity. NPO VOSTOK in Novosibirsk
developed appropriate technological process for the MSGC plates
production and good quality of the chambers produced was demonstrated.
At present the main problem of the proposed technology is the
thickness of the substrate which has to be made of 100 mm thick
(MSGCs which were fabricated by BINP use 0.5 mm glass). We are
developing pulling technology which will permit us to get thin
semiconductive glass substrates cheaply and in large quantities.
We plan to construct MSGCs on thin conductive glass substrates
and test them at CERN in 1995. At the same time we are planning
to begin production of the set of masks for wedge shaped detector
with radial strips in order to begin (in the second half of the
year), production of such MSGC plates and perform its tests by
the end of the year. One of the main subjects of the R&D for
the 1995 will be radiation hardness of the MSGC plates in a more
real environment. Together with a group from Brussels University
we are planning to perform tests in intensive X-ray beam.

On the basis of 1995 R&D results the final technology of
MSGC will be chosen for the final design. RDMS group interested
in Tracker detector will then work on the chosen baseline. The
MSGCs can be produced in Novosibirsk and Brussels and will be
tested in the prototype of the sector of the wheel. In 1996 assembling
and testing of some limited size prototype will be continued and
in 1997 we are planning together with other participants of forward
tracker to assemble the prototype of the forward wheel.